High capacitance single layer capacitor

ABSTRACT

A high capacitance single layer ceramic capacitor structure having a ceramic dielectric body containing one or more internal electrodes electrically connected to a metallization layer applied to the side and bottom surfaces and a metallization pad electrically isolated from the metallization side and bottom surfaces positioned on a top surface of the ceramic body.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to single layer capacitors, and moreparticularly, to high capacitance single layer ceramic capacitors and amethod of making the capacitors.

Single layer ceramic capacitors have a useful form factor for assemblyinto electrical circuits which are present on printed circuit boards orintegrated circuits within chip carriers or other packages where spaceis limited. Dimensions of the ceramic capacitor can be matched with thelimitations within the printed circuit board or chip carrier holding theintegrated circuit. Typically the bottom surface of a ceramic capacitoris soldered to or connected with conductive epoxy to the surface of theprinted circuit board and the top face of the ceramic capacitor presentsone or more electrically conductive pads that serve as another circuitconnection end point. Typically, single layer ceramic capacitors areproduced by metallizing two faces of a thin sheet of sintered ceramicmaterial. The metallized ceramic sheet is then cut to size by sawing orabrasive cutting techniques. While the form factor of these capacitorsis desirable, the amount of capacitance that can be achieved limitstheir usefulness in certain applications, particularly when designconsiderations require particularly small or particularly thincapacitors. In such circumstances, the capacitor does not havesufficient structural strength to withstand undesirable fracturing orchipping during routine handling during assembly into circuits.Consequently design tradeoffs must be made between using thicker ceramiclayers for greater strength and thinner ceramic layers for greatercapacitance.

2. Description of Related Art

Prior attempts to achieve higher capacitance in a single layer capacitorwhile maintaining structural strength include using a flat, horizontalcapacitor with metallization on its lower side having a gap. The problemwith this design is that it creates unwanted resonances at frequenciesabove a few gigahertz. Another approach has been to use standingdielectric chips with opposed metallized surfaces and with metal leadsattached to the respective surfaces. Problems with this design is thatleads are fragile and require extreme care during fabrication, shipping,handling and soldering in place to traces. In addition, standing leadedcapacitors produce significant signal resonances, especially forfrequencies above a few gigahertz. Further attempts to produce highercapacitance single layer capacitors include multi-layer materialslaminated together. These multi-layers include a ceramic dielectricmaterial and a ceramic/metal composite material sheet. A problem withthis design is that the manufacturing process includes laminating sheetstogether and the ceramic/metal composite material is quite expensive.Yet another ceramic capacitor design includes at least one interiormetallization plane or plate and a multiplicity of vias performingmultiple redundant electrical connections within the capacitor. Suchdesigns are extremely difficult to manufacture to provide for interiormetallization planes or plates connected through a multiplicity of vias.

Consequently, a need exists for a high capacitance single layer ceramiccapacitor which is inexpensive and easy to manufacture.

SUMMARY OF THE INVENTION

The present invention provides a monolithic single layer capacitorhaving high capacitance and structural strength which is easily andinexpensively manufactured. The capacitor of the present inventionprovides for electrical connections to be made on top and bottomopposing surfaces. The capacitor provides for higher capacitance valuesthan with existing designs while still maintaining form factor and highstructural strength. The ceramic capacitor includes a continuousmetallization applied to one to five surfaces of a ceramic body whichmakes contact within one or more internal electrodes. One or morefurther metallization pads are applied to the top surface of thecapacitor. Electrical connection to an external circuit are achieved byattaching to the top and bottom surfaces of the capacitor. The capacitorcan be manufactured through the use of a green ceramic bar which isbuilt upon with one or more internal electrodes. The bar is cut andindividual chips fired. The capacitor is metallized on all sides and thetop pad is formed by removal of a portion of the metallization using alaser, mechanical milling or other process to isolate a top conductivepad. Alternatively, a passivation material on the surface of thecapacitor can be applied prior to isolate the top conductive pad.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a single layer capacitor of the presentinvention;

FIG. 2 is a cross-sectional view of the capacitor of FIG. 1;

FIG. 3 is a cross-sectional view of an alternative single layercapacitor of the present invention;

FIG. 4 is a perspective view of another alternative embodiment singlelayer capacitor of the present invention;

FIG. 5 is a perspective view of another alternative embodiment singlelayer capacitor of the present invention;

FIG. 6 is a cross-sectional view of the capacitor of FIG. 5;

FIG. 7 is an electrical schematic of the capacitor of FIG. 5; and

FIG. 8 is a cross-sectional view of another alternative embodimentsingle layer capacitor of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIGS. 1 and 2, the present invention provides a highcapacitance surface mountable single layer ceramic capacitor 10 havinghigh structural strength which is easy and inexpensive to manufacture.The capacitor includes a ceramic dielectric layer 12 having a partial orcontinuous metallization layer 14 applied to all four side surfaces 16,18, 20, 22 and bottom surface 24. The dielectric layer 12, also referredherein as the ceramic body, includes an internal electrode 26 whichextends across an entire width of the ceramic body and is in electricalcontact with the metallization layer 14, as shown for example in FIG. 2on either side 16 and 20. The capacitor further includes a metallizationpad 28 positioned on the top surface 30 of the ceramic body 12.

Electrical connections to an external circuit can be made by attachingto the top metallization pad 28 and the bottom metallization layer 14 onthe bottom surface 24 or to sides 16, 18, 20 and 22. The capacitancevalue within the capacitor can be described by the formula C=eA/d wheree=the permittivity of the dielectric body material, A=the area of thetop pad 28, and d=the distance between the top pad 28 and the electrode26. Unlike standard single layer capacitors, the distance d can beminimized without compromising structure and strength of the componentby the inclusion of the electrode. The distance d is smaller because thepositioning of the electrode yet the strength of the capacitor isachieved by having a thickness of material below the electrode.

Although FIGS. 1 and 2 illustrate a single layer ceramic capacitorhaving a single electrode 26, multiple electrodes can be incorporated asshown in FIG. 3 wherein capacitor 32 includes two or more electrodes asshown by 34 and 36 positioned within the ceramic dielectric body 38.

The capacitor can be manufactured by using a green ceramic bar, andbuilt upon with one or more internal electrodes by positioning theelectrodes in between individual layers of ceramic dielectric material.The ceramic material can be Class 1, 2 or 3 ceramic or any other ceramicdeemed suitable for manufacture of multi-layer ceramic capacitors orsingle layer capacitors. The resulting fired capacitor is a single layerdielectric which is then metallized on all six sides by plating. The toppad 28 is then formed by removing the outer portions of themetallization from the top surface using a laser, mechanical milling orother technique to create the top conductive plate.

Alternatively, as shown in FIG. 4, prior to metallizing, a passivationsurface such as a non-plateable glass or other insulating material 40can be applied onto the top surface 30. The bar is then cut intodiscrete components. When the capacitors are metallized, the passivationmaterial creates a gap between the plated sides and the top pad 28. Thepassivation material creates the gap between the top conductive plateand the bottom metallization that is connected to the internalconductive electrode. FIGS. 1 through 4 illustrate a square capacitor,however, as shown in FIG. 5, a capacitor 42 can be rectangular and cancontain a number of top conductive pads 44, 46 and 48. The size of pads44 through 48 can be the same or different. Utilizing a plurality ofconductive pads can create a capacitor array wherein the pad sizes canbe altered, or customized so that each capacitor value 50, 52 and 54 canbe different as shown in FIG. 7.

FIG. 8 illustrates yet another embodiment single layer capacitor 60 ofthe present invention. Capacitor 60 is a floating capacitor which is twocapacitors in series. Capacitor 60 includes a ceramic body 62 havingelectrodes 64 and 66 positioned therein similar to FIG. 3. Metallizationlayer 68 is applied to all four sides of the ceramic body andmetallization pad 70 is positioned on the top surface 72 and ametallization pad 74 is position on bottom surface 76 of the ceramicbody. Pads 70 and 74 are formed similar to the pads in the otherembodiments.

The capacitor of the present invention, for example is not restricted tobut can have dimensions ranging from 0.010″×0.010″ to 0.090″×0.090″ forsquare versions and is not restricted to but can have thicknessesranging from 0.003″ to 0.020″. Some of the advantages of the presentinvention include higher capacitance per volume and the ability to usevarious dielectrics which result is a wide capacitance range. Thecapacitor eliminates the need for high cost materials and provides theability to make an array of single layer capacitors of any size anddifferent capacitance values within the same capacitor strip. Thecapacitor of the present invention further allows the capacitance valuesto be customized, and the utilization of thin dielectric layers toprovide high capacitance values without sacrificing structural strength.

Although the present invention has been described and illustrated withrespect to several embodiments thereof, it is to be understood thatchanges and modifications can be made therein which are within the fullintended scope of the invention as hereinafter claimed.

What is claimed is:
 1. A high capacitance single layer ceramic capacitorcomprising a single layer ceramic dielectric body having at least oneinternal buried electrode extending across an entire width thereof inelectrical contact with a conductive metallization layer positioned onat least a portion of each of the four sides and an entire bottomsurface of the single layer ceramic dielectric body, and at least oneelectrically isolated metallization pad positioned on a top surface ofthe single layer ceramic dielectric body and electrically isolated fromall electrodes inside the single layer ceramic dielectric body, whereinthe electrically isolated metallization pad is in parallel with a mainsurface of the internal buried electrode, and formed only on a topsurface of the ceramic dielectric body.
 2. The capacitor of claim 1,further having two or more electrodes spaced within the single layerceramic dielectric body.
 3. The capacitor of claim 1, wherein there area plurality of metallization pads electrically isolated from one anotheron the top surface of the capacitor.
 4. The capacitor of claim 3,wherein the metallization pads are different sizes.
 5. A highcapacitance single layer ceramic capacitor comprising a single layerceramic dielectric body having at least one internal buried electrodeextending across an entire width thereof in electrical contact with aconductive metallization layer positioned on at least a portion of eachof the four sides, said capacitor further comprising a metallizationlayer on an entire bottom surface of the single layer ceramic dielectricbody, and at least one electrically isolated metallization padpositioned on a top surface of the single layer ceramic dielectric bodyand electrically isolated from all electrodes inside the single layerceramic dielectric body, wherein the electrically isolated metallizationpad is in parallel with a main surface of the internal buried electrode,and formed only on a top surface of the ceramic dielectric body.